Tamoxifen: reduced effectiveness when used with CYP2D6 inhibitors

01 September 2011

Tamoxifen is a medicine used to treat breast cancer. In order to work, tamoxifen is metabolised (broken down) by an enzyme called cytochrome P450 isoenzyme 2D6 (CYP2D6).

Some medicines block the function of CYP2D6 and may therefore interfere with the actions of tamoxifen, making it less effective in treating breast cancer. The scientific and clinical evidence for this issue has been assessed and is summarised in this Public Assessment Report.

The assessment concluded that the use of medicines that are known to be strong or potent CYP2D6 inhibitors should be avoided in patients taking tamoxifen. Examples of such medicines are: paroxetine; fluoxetine; buproprion; quinidine; cinacalcet.

This report presents the evidence that was available when the regulatory decision was made, showing a ‘snapshot’ of the clinical landscape at the time. However, any advice in this report remains current unless it is superseded by a more recent report (where relevant, this is indicated).

Page last modified: 11 February 2016